Electronic structure and spin-state transition ofLaCoO3

Abstract

We present soft-x-ray-absorption spectra (XAS) of ${\mathrm{LaCoO}}_{3}$ taken at different temperatures (80--630 K). The shape of the multiplets in the Co 2p XAS spectra conveys information on the symmetry and spin of the ground state. The O 1s XAS spectra are related to unoccupied metal bands through covalent mixing. The changes in the spectra taken at different temperatures provide information on the spin-state transition in this compound. At low temperature, 80 and 300 K, the material is in a highly covalent low-spin state. The main contribution to the ground state in this case is given by ${\mathit{t}}_{2\mathit{g}}^{6}$${(}^{1}$${\mathit{A}}_{1}$) with an occupancy of 0.56. At higher temperature, 550 and 630 K, the results indicate a gradual transition to a mixed-spin state. The main contribution to the high-spin part of the mixture is given by ${\mathit{t}}_{2\mathit{g}}^{4}$${\mathit{e}}_{\mathit{g}}^{2}$${(}^{5}$${\mathit{T}}_{2}$) with an occupancy of 0.71. There is no evidence of charge disproportionation in the temperature range 80--630 K. The O 1s XAS spectra reflect important changes in the unoccupied Co 3d bands across the spin-state transition.